In a communication system including Micro-Processing Units (MPUs) that perform data processing and that have different control targets; a buffer is installed so as to temporarily store data which is to be communicated among the MPUs performing coordinated operations, so that the differences in the processing speeds and the transfer speeds among the MPUs are compensated. In such a communication system, at the time of communicating data among the MPUs having different bus widths of the data bus, the data transfer speed can be enhanced.
However, in the communication system mentioned above, the buffer merely provides the function of storing the data. Thus, even if abnormal data that is attributed to abnormality occurring while reading data from or writing data in the buffer is sent to the receiver MPU, neither the sender MPU nor the receiver MPU can confirm the presence or absence of data abnormality. Thus, abnormal data attributed to abnormality in the buffer gets transferred.